docs: def get_extra_data(self, data):
          """Get eventual extra data for this placeholder from the
          admin form. This method is called when the Page is
          saved in the admin and passed to the placeholder save
          method."""
          result = {}
          for key in list(data.keys()):
              if key.startswith(self.ctype + '-'):
                  new_key = key.replace(self.ctype + '-', '')
                  result[new_key] = data[key]
          return result